Microorganisms are known to proliferate in many different liquids, particularly where larger volumes of such liquids are contained within receptacles which are predominantly or exclusively adapted only for storage or containment, and within which the liquid is only relatively infrequently exchanged, replenished and/or depleted. In the particular case of storage tanks which are generally closed to the atmosphere, as most are, often there is some stagnation of both the liquid they contain and the air or other gases which fill the remainder of the tank above the liquid. Proper cleaning of such tanks is inconvenient and often difficult, particularly when the tank forms part of a critical liquid supply system, because cleaning processes such as sterilisation and decontamination usually require that the tank be completely purged of its contents so that dedicated cleaning equipment and chemicals can be applied internally of the tank.
To provide a first example, the presence of microorganisms in fuel storage tanks is a problem that has affected the oil industry for many years. Microorganisms present within such tanks are known to feed on petroleum fractions at the water/fuel interface, which in turn promotes the formation of sludge and acidic residues which block and corrode components of the tanks respectively. The presence of sludge and/or acidic residues in the tank can also, in certain instances, adversely affect the quality of the fuel, the shelf life of the storage tank or longevity of the engine in which the fuel is used. The above problems are especially prevalent in storage tanks which comprise crude oil, diesel fuel or kerosene.
To date, biocides such as methylene-bus-oxazolidine (MBO) have been used to control microbial growth. However, biocides are expensive, and in the case of MBO, certain microorganisms have already developed a resistance so that the use of MBO is becoming less suitable as a means for both controlling the growth of, and eliminating microorganisms in fuel storage tanks and engines.
In order to minimise CO2 emissions more environmentally friendly fuels, e.g. biofuels, are now being used, either alone or in combination with conventional petroleum fuels as part of a blend. Biodiesel is a well-known biofuel that is currently being used as an alternative to conventional petroleum fuels. However, fuels which comprise biodiesel suffer from the disadvantage that they are more susceptible to microbial contamination because biodiesel, as well as containing small amounts of water, is hygroscopic, i.e. it attracts and stores water from the surrounding environment. Thus there is a tendency for microorganisms to proliferate to a greater degree in storage tanks containing biodiesel than there is in tanks containing conventional petroleum fuels.
Biodiesels also suffer from the disadvantage that increased concentrations of NOx are produced as a result of the fuel combustion process. NOx emissions are known to be harmful to human health and contribute to the formation of smog in the atmosphere.
Accordingly, it is an object of embodiments of the present invention to provide a means for controlling microbial growth in fuel storage tanks and engines.
Other examples of liquid storage prone to microorganism proliferation include cooling water tanks which supply oil refineries and other chemical plants, thermal power stations and heating ventilation and air-conditioning (HVAC) systems, swimming pools, and cooling towers (both natural and induced draft). In particular, cooling towers are essentially heat rejection devices which reject waste heat to the atmosphere through the cooling of a water stream to a lower temperature. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or, in the case of closed circuit dry cooling towers, rely solely on air to cool the working fluid to near the dry-bulb air temperature. Cooling towers vary in size from small roof-top units to very large hyperboloid structures commonly seen adjacent power stations, but in essence, all such towers employ water as the coolant, and as such that water is commonly contained in a large receptacle in which conditions for microorganism proliferation are often optimised.
As far as the storage and/or containment of water is concerned, inhibiting microorganism proliferation is important if not critical because of the potential that humans may come into contact with contaminated water. For example, there have been many publicised outbreaks of Legionnaire's disease in hospitals, and such have been traced to the existence of the “legionella pneumophila” microorganism in water storage tanks in and around the hospitals where outbreaks have occurred. In swimming pools, microorganism proliferation can result in a biofilm on the water surface, which at the very least is aesthetically off-putting, and at worst has potentially harmful health implications. Although the chlorination of water can provide some resistance to microorganism proliferation in standing bodies of water (including possibly drinking water reservoirs), the use of chlorine is being increasingly disparaged as it has been suggested that chlorine may be the root cause of various short and long term neurological disorders.
Accordingly, it is an object of embodiments of the present invention to provide a means for controlling microbial growth in liquid storage receptacles and tanks, particularly those adapted for storing or containing water or fuels, and in the liquids themselves commonly contained in such receptacles and tanks.
It is also an object of embodiments of the present invention to provide an alternative to conventional biocides for controlling the growth of microorganisms in liquid storage receptacles and tanks, and in the liquids contained therein.
It is also an object of embodiments of the present invention to provide an alternative to biocides for controlling the growth of microorganisms in fuel storage tanks and engines.
It is another object of embodiments of the present invention to reduce water absorption in fuels, and in particular fuels that comprise biofuels such as biodiesel.
It is a further object of embodiments of the present invention to reduce NOx emissions resulting from the combustion of fuels containing biodiesel.